This invention relates generally to an electronic or semiconductor device package structure and, more particularly, a package for a semiconductor device as a hermetically sealed unit.
Semiconductor devices employed in high current type applications, commonly referred to as power devices, generate a substantial amount of heat in operation of the device. In the past it has been very common to have a package known as a TO-3 package, which essentially had a large heat sink area, the die being encapsulated by a metal cap, while the leads were brought out through metal-to-glass seals. If demand calls for a package which must be electrically isolated, a ceramic substrate has to be placed in the package and, if the package was a power package and had to dissipate heat, the ceramic substrate would generally be beryllium oxide, and in order to help to dissipate the heat, that is spread it, an efficient means must be provided in contact with the substrate. Whatever this means may be, it must not stress the substrate by differences in thermal expansion coefficients. The commercial acceptability, therefore, of such devices is based upon their ability to dissipate the generated heat at a high rate as excessive heat retention can destroy the semiconductor die within the device.
Miniaturized packages, whether they be a high power device or a low power device, still have to dissipate heat. Problems arise because there is a linear coefficient of expansion of the semiconductor die of approximately 3.5.times.10.sup.-6, and this has to be closely matched in some way to the material upon which the die is mounted or there will be undue stresses developed which can cause failure of the die or create die attachment reliability problems.
Another consideration is fabrication of the unit as it is desirable to simultaneously perform soldering operations.
Another problem with prior art semiconductor packages has been the power loss problem and inductance in the leads as the operating frequency is increased. This is due in part to the use of poor conductors and conductors of a small size that lead away from the die. The present invention accordingly has the object to eliminate these problems for radio frequency operation by utilizing rectangular copper clad conductors which are useful to one 1 GHz.
It is, therefore, a primary object of this invention to obviate some of the foregoing problems inherent in prior art packages.
It is a further object of the invention to provide a structure for a package of a semiconductor device which closely matches the thermal coefficients of expansion while providing good heat dissipation and electrical insulation.
It is another object of the invention to provide a semiconductor package having terminals which permit it to be mounted directly on a circuit board with the heat sink dissipating area mounted on top of the package spaced from the board in what is commonly termed "surface mount".
It is still another object of the invention to provide a semiconductor package where the package may be mounted on a circuit board in a vertical direction where the heat sink rises vertically from the board in surface or through board fashion.
Another object of the invention is to provide a package wherein the connections can be preformed in one step and the cover may be attached in a subsequent step without destroying the previous connection joints.